1. Field of the Invention
This invention relates generally to the field of disc drive data storage devices and more particularly, but not by way of limitation, to a latch housing for mounting and supporting a latch mechanism for latching the moving head carriage of the disc drive and dissipating some of the kinetic energy of the moving carriage.
2. Brief Description of the Prior Art
Systems to absorb the kinetic energy of mechanical shocks generated by contact with a moving body are well known in the art. The simplest of such systems include some type of deformable member which deflects from its original position or shape in response to impact from a moving body.
If the system is intended for "one-time" use, the deformable member may be permanently altered. An example of such a system is the "crushable" bodywork of certain current automobiles, which are designed to absorb the destructive force of a collision, while diminishing the force transferred to occupants of the vehicle.
Other common systems include some type of resilient member designed to deform at impact and return to its original condition after the kinetic energy of the contact has been absorbed. An example of, perhaps, the simplest of this type of shock absorption system is a rubber block mounted in the path of a moving object--such as a swinging door--which deforms at impact and "bounces back" to its original shape. Other examples of this type of mechanical shock absorption systems are easily recalled, including those which incorporate springs, cantilevered beams and other resilient members.
Most simple systems which include resilient members, though, operate under the assumption that the resilient member can be allowed to deflect--or deform--in the original direction of movement of the moving body and then "spring" back past the original shape or location of the resilient member, before returning--after perhaps several iterations of this oscillation--to the original, or neutral, position. This is indeed an acceptable response in these systems.
There are, however, cases in which such "bouncing" about a neutral position is unacceptable, i.e., in which the system may be permitted to deflect only in the direction of movement of the moving body, and must then return to the neutral position without passing the original point of contact.
One such situation is found in the carriage latching mechanisms of disc drive data storage devices.
Disc drive data storage devices of the type commonly referred to as "Winchester" disc drives record--or write--and retrieve--or read--digital data on a magnetic medium deposited on the surfaces of rotating rigid disc members. During operation, the air pulled along by the spinning discs interacts with self-acting hydrodynamic air bearing surfaces on read/write heads to "fly" the heads in close proximity to the discs, thus eliminating any contact-induced wear on or damage to the heads or discs. An actuator mechanism is typically employed to controllably move a vertically aligned array of read/write heads--one per disc surface--to any desired one of a plurality of circular, concentric data tracks on the discs. The rapidity of this movement--or seek time--is one of the principal criteria by which the performance of the disc drive is judged. The quest for minimal seek time has lead to one of the greater challenges facing a designer of disc drives. Current high performance disc drives utilize voice coil motors to move the heads from track to track, and have achieved average seek times of less than ten milliseconds (0.010 seconds) with great reliability. Such seek performance requires that the actuator achieve extremely high velocities. For instance, a high-performance disc drive of the current technology using a rotary voice coil actuator typically achieves radial velocities of 220 radians per second. Even though the moving mass of the actuator is minimized by design, speeds of this order create a significant problem for the designer.
Moving-coil voice coil motors incorporate a coil of wire suspended within the field of a permanent magnet--or array of magnets--and constrained by some type of mechanical attachment mechanism which defines and restricts the coil's direction and extent of motion. When DC current is applied to the coil, an interaction occurs between the magnetic field induced about the coil and the magnetic field of the permanent magnets, in accordance with the well known Lorenz relationship. If, however, power is removed from the coil--as is the case when power is interrupted to a disc drive--the coil is free to move in an uncontrolled manner within the range defined by its mechanical attachment mechanism. Such uncontrolled motion of the voice coil motor in a disc drive data storage device is entirely unacceptable, since the loss of power to the actuator implies simultaneous loss of power to the motor spinning the discs, and thus potentially damaging contact between the heads and discs.
Because of this characteristic of voice coil actuators, the common practice in the industry is to move the heads to a preselected position--or park zone--when any loss of power is detected, and latch the actuator in this position until power is restored. Obviously, since the parking sequence occurs in response to a loss of power, the speed of the actuator during the parking sequence must be maximized, which, in turn, implies that a high level of kinetic energy must be dissipated by the latching mechanism. Further, the challenge is to absorb this kinetic energy, and, at the same time, prevent the heads from oscillating back and forth while direct contact between the heads and discs is possible due to the deterioration of the air bearing.
The features of the present invention are particularly suited to the above described application, since it is capable of absorbing and dissipating the kinetic energy of a moving body by deflecting from a neutral position in response to contact with the moving mass, and includes a mechanism for limiting the extent of motion of the system to a return to the neutral position after such contact and deflection.